Today's wireless telecommunications networks provide telephone subscribers with the ability to access telecommunications services from almost anywhere in the world. The key to facilitating such world-wide access is mobility management. With mobility management, wireless networks are able to track the location of mobile stations so that mobile services can be delivered to them.
Wireless networks are currently transitioning from an architecture referred to as Third Generation (3G) to a 4G (Fourth Generation) architecture, commonly known as LTE (Long Term Evolution). Each of these architectures have different mobile devices, or user equipment (UE), as well as different network devices that provide wireless service for the UEs. As the transition from 3G to LTE is implemented, it is necessary to provide a system for delivering 3G CS calls for LTE UEs which are CS capable. This call delivery occurs via a combination of 3G and LTE network devices. This system is commonly called Circuit Switched Fallback (CSFB).
A 3G CS wireless network is typically formed of a number of cells, each covering a small geographic area within which a UE, may receive mobile services. Each cell is equipped with a base station that provides radio coverage to the cell, thereby enabling communication with UEs located within the cell. By integrating the coverage of multiple base stations, a wireless network is able to provide radio coverage to mobile stations over a large geographic area.
The coverage area of a collection of neighboring base stations in a 3G wireless network is commonly referred to as a location area each served by a mobile switching center (MSC). The MSC is the network node that provides circuit-switched calling, mobility management and other telecommunications/mobile services to UEs. In particular, the MSC maintains subscriber data for all UEs that are currently located within one of the location areas served by the MSC. UE subscriber data is permanently maintained in a home location register (HLR) within the wireless network. When the UE is within the range of an MSC, that MSC acquires a copy of the UE subscriber data from the HLR and maintains it in a visiting location register (VLR). The location area of the UE is also maintained in the visiting location register (VLR) for the MSC to page the UE in the location area for a mobile termination call. An MSC that is associated with the current location area of a UE is referred to as a visiting mobile switching center (VMSC) relative to the mobile station. The MSC receiving a call that is intended for the UE subscriber is referred to as a gateway mobile switching center (GMSC).
When a call from a calling UE is received at a GMSC, the HLR of the called UE is consulted to see what VMSC is currently serving the called UE, then the HLR requests a roaming number from the VMSC using a Provide Roaming Number (PRN) message. The VMSC provides a roaming number to the HLR with a PRN Acknowledge message. The GMSC uses the roaming number, received from the HLR, to send an Initial Address Message (IAM) to the VMSC after which the VMSC pages the called UE. When the called UE is an LTE device, the VMSC sends the paging request to a mobile management entity (MME) which is responsible for managing tracking and paging procedures in the LTE wireless network. When a 3G CS call for a called LTE UE originates in a 3G network, the interaction between 3G network devices such as MSCs and LTE network devices like the MME is managed by a set of procedures using CSFB.
Normally, the call setup procedure described above results in a call path being set up through the wireless network to the termination MSC and then the UE is paged. In some circumstances, this call path may turn out to have been unnecessary if the UE does not accept the call, resulting in inefficient use of network resources.
One solution to this situation in the prior art is prepaging, where the UE is paged during the PRN procedure, i.e., before the VMSC returns the PRN Ack message the GMSC. Unfortunately, prepaging does not work with CSFB.
Therefore, what is needed is a procedure for performing CSFB signaling in a wireless network with prepaging.